A retrospective Penn Medicine analysis found lower breast cancer incidence among women with documented GLP-1 medication exposure. The results were presented at the 2026 American Society of Clinical Oncology Annual Meeting and published in JCO Oncology Practice.
The study included 111,646 women ages 45 to 80 with a BMI of 25 or above, breast imaging records, and a documented outcome in the Penn Medicine electronic health record between January 2022 and June 2025.
Of the full cohort, 15,264 women had documented GLP-1 prescriptions and 96,382 had no documented GLP-1 exposure.
Researchers analyzed breast cancer incidence in the full cohort and in a matched cohort of 30,528 women. The matched analysis used 1-to-1 controls for each GLP-1 case across age, race, ethnicity, BMI, breast density, and diabetes status.
Lower breast cancer incidence was seen in both analyses. Penn Medicine reported 35.1% lower odds in the full analysis and 30.5% lower odds in the matched cohort.
The American College of Radiology described the study as ACR-managed and said GLP-1 users were up to 35% less likely to develop breast cancer than women who did not take GLP-1 drugs.
Elizabeth McDonald, MD, PhD, professor of radiology at the University of Pennsylvania Perelman School of Medicine, led the study. ACR said Etta D. Pisano, MD, FACR, served as senior author, and Laura Gillis, PhD, served as study statistician.
The findings remain observational. Penn Medicine said the study did not account for type of GLP-1 medication, length of use, genetic risk factors, or cancer stage or type at diagnosis.
“Prospective data-the gold standard in clinical research-is lacking,” Penn Medicine noted.
McDonald and collaborators are working to develop a multisite clinical trial to assess whether GLP-1 medications can lower breast cancer incidence among women at high risk, including women with a history of breast cancer.
ACR urged funding for a large prospective study to clarify whether GLP-1 medications have an incidence or prevention benefit in breast cancer.
Company:ACR
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